Research On The Key Technologies For Laser Beam Array Combining System

The invention of the first operational laser in 1960 greatly inspired the development of high-energy laser projects around the world.At present,the lasers used in domestic and foreign research mainly include fiber lasers,semiconductor pumped solid-state lasers,free electron lasers,and liquid lasers.Fiber lasers have the advantages of high conversion efficiency,compact structure,high beam quality,and convenient thermal management,making them the preferred laser source in recent years.Due to nonlinear effects and thermal effects,a single fiber has a limit on the output power,and it is difficult to ensure beam quality at high power.If a higher output power level is desired,multiple lasers need to be combined.Laser beam array combining based on adaptive optics can guarantee higher beam quality when increasing output power.At the same time,the optical fiber array system used in laser transmission can overcome the shortcomings of the traditional single telescope optical system with large quality,large volume and high price.The key technologies of the laser beam array combining system are mainly focused on phase control and tip-tilt control.The tip-tilt control technology of beam was a research hotspot in laser beam array combining in recent years.By directly controlling the translation of the laser beam on the focal plane of the collimating lens to achieve the deflection of the output beam,researchers at home and abroad have proposed different tip-tilt control schemes,mainly divided into bimorph piezoelectric driver and piezoelectric direct driver.In this paper,the wavefront tip-tilt control mechanism(fiber positioner)was used to carry out related research on the magnification,dynamic range and frequency response,as well as the optimization algorithm of phase lock control and tip-tilt compensation.In this paper,the laser beam array combining is studied by theoretical analysis and numerical simulation.Based on this,a fiber positioner based on flexible hinge amplifying mechanism was designed to replace the traditional deforming mirror as a wavefront correction component for wavefront tip-tilt phase compensation.The theoretical derivation and simulation analysis of the relationship between the input signal and the corrected displacement was done,the relevant system model was established,the ability of wavefront aberration correction for the fiber positioner based on the flexible hinge amplification mechanism was verified by laser beam array combining experiment.The main contents of this paper include the following aspects:1.The mathematical model of laser beam array combining was established.The main factors of the array beam combination transmission mechanism and the beam combining effect were analyzed,and the beam intensity distribution and beam quality were calculated.The power density in the bucket was proposed for beam quality performance metric in the laser beam array combination.2.A fiber positioner based on flexible hinge amplifying mechanism was proposed to replace the traditional deforming mirror as the wavefront correcting component,and related structural design and theoretical analysis were carried out.Static and dynamic analysis of the amplifying mechanism was performed to derive the magnification and the resonant frequency was analyzed.The relationship between input and output corrected displacement was derived.3.The adaptive optics system based on system performance metric optimization was analyzed.The stochastic parallel gradient descent algorithm was selected as the control algorithm of laser beam array combining analysis.The stability and convergence speed were analyzed,and the closed-loop control and distortion compensation capability of the algorithm were verified.The gain coefficient and the random disturbance amplitude,which influence the iteration and convergence are proposed optimization.4.A polarization maintaining fiber laser system was designed and laser beam combining phase control experiments was carried out to analyze the effects of laser line width,power,fiber extrusion,environmental vibration and other factors on the single beam,the phase adjustment capability of the phase shifter was verified.The effects of beam angle,optical path difference(phase difference),power difference and other factors on beam combining were analyzed.5.The laser beam array tip-tilt experimental platform was build,carrying out the positioner performance test,including the dynamic deflection range and frequency response curve.After analysis we figure out that driving fiber connector is more difficult than directly driving the bare fiber,resulting in the positioner dynamic range decreasing,which can provide a reference for the subsequent structure improvement.The fiber positioner was used as the wavefront correction component to perform the beam tilt compensation experiment.The result proved the ability of the fiber positioner based on the flexible hinge amplifier to compensate the wavefront distortion.Based on theoretical analysis,numerical simulation and experimental data,further improvements for the structure of the fiber positioner and the beam combining system is possible.